1. Field of the Invention
The invention relates to a key device for a vehicle which compares ID code information preset in a key with ID code information preset in a vehicle, thereby allowing an engine of the vehicle to be started.
2. Description of the Related Art
FIGS. 13 and 14 show a first prior art key device for a vehicle which is disclosed in, for example, Japanese Patent Examined Publication No. Hei 4-15141. In the figures, reference numeral 51 designates a key cylinder disposed on a cover of a steering column which is not shown. A hole 53 into which a tip portion 52a of a key 52 enters is formed in the key cylinder 51. The key cylinder 51 has an annular fixed rotor case 54. A columnar rotor 55 is rotatably attached into the rotor case 54.
A key insertion slot 56 which communicates with the hole 53 of the key cylinder 51 is formed in the rotor 55. An annular core 57 is disposed in the rotor case 54 surrounding the rotor 55. The annular core 57 is partly exposed toward the inlet of the key insertion slot 56. As illustrated, vehicle coils 58 and 59 are wound on the annular core 57 in the same direction so that induction magnetic fields are generated in a direction perpendicular to the key rotation axis X--X of the key 52.
On the other hand, a stem-like core 60 which cooperates with the annular core 57 to form a magnetic circuit is attached to a grip portion 52b of the key 52. A key coil 61 which is to be magnetically coupled with the vehicle coils 58 and 59 is wound on the stem-like core 60. A series resonance circuit K1 consisting of a capacitor C1 and a coil L1 is connected to the key coil 61. A series resonance circuit K2 consisting of a capacitor C2 and a coil L2 is connected in parallel to the series resonance circuit K1.
The capacitances of the capacitors C1 and C2, and the inductances of the coils L1 and L2 are set in such a manner that the resonance frequencies f1 and f2 of the series resonance circuits K1 and K2 are different from each other.
Next, the operation will be described.
When the key 52 is inserted into the key insertion slot 56 of the key cylinder 51, a signal for ID code detection is supplied to the vehicle coils 58 and 59. The signal is a sinusoidal signal of a constant voltage and its frequency is changed from a lower one to a higher one in a predetermined range. The key coil 61 receives the frequency signal for ID code detection through the annular core 57 and the stem-like core 60. When the frequency of the received signal coincides with one of the resonance frequencies f1 and f2 of the series resonance circuits K1 and K2, a current flowing through the key coil 61 is increased in level.
The vehicle coils 58 and 59 detect the resonance frequencies f1 and f2 at the timing when the current level is increased. The ID code information preset in the key 52 is read on the basis of the detected resonance frequencies f1 and f2. It is judged whether the read ID code information coincides with vehicle ID code information stored in a ROM (not shown) or not. Only when coincidence is attained, a signal allowing the start of the engine is output so that the engine is enabled to be started.
FIGS. 15 and 16 show a second prior art key device for a vehicle which is different from the above-described prior art example. The reference numeral 71 designates a vehicle coil configured by winding a coil wire by a predetermined number of turns in an annular groove which is formed on the outer peripheral face of a cylindrical bobbin 72. The ends 71a and 71b of the vehicle coil 71 are connected to an electric circuit of the vehicle through lead wires 73a and 73b in a terminal section 72a which is integrated with the cylindrical bobbin 72.
The cylindrical bobbin 72 is inserted into a key cylinder 74, thereby causing the terminal section 72a to elongate in parallel with the cylinder axis or the key rotation axis X--X and toward the mounting base of the key cylinder 74. The cylindrical bobbin 72 is engaged with the outer periphery of the key cylinder 74 on the side of a key insertion slot 81, so as to be attached thereto. Therefore, an induction magnetic field generated by the vehicle coil 71 is generated in parallel with the key rotation axis X--X.
The first prior art key device for a vehicle is configured so that the induction magnetic fields due to the vehicle coils 58 and 59 are generated in a direction perpendicular to the key rotation axis. Therefore, the key coil 61 is not magnetically coupled with the vehicle coils 58 and 59 unless the key coil is near the vehicle coils. Consequently, strong induction magnetic fields must be generated. This produces a problem in that the vehicle coils 58 and 59 must have a large number of turns and their sizes are increased.
In the second prior art key device for a vehicle, as shown in FIG. 17, the vehicle coil 71 which is powered by a power supply circuit 78 after a key 75 is inserted into the key insertion slot 81 generates the induction magnetic field in parallel with the key rotation axis X--X. Even a key coil 75a disposed in the key 75 is not near the vehicle coil 71, therefore, the coils can be easily magnetically coupled with each other. When the key cylinder 74 is not disposed horizontally or elongates slantingly, however, the induction magnetic field is at the same time applied also to a key coil 76a disposed in another key 76 for a vehicle which is attached to a key holder 77. Therefore, ID code signal generating circuits 75b and 76b of the two keys 75 and 76 transmit ID code information through the key coils 75a and 76a, and the vehicle coil 71 simultaneously receives the different kinds of code information respectively transmitted from the keys 75 and 76. As a result, an ID code-information receiving and decoding circuit 79 of the vehicle which receives the different kinds of code information produces confusion in the decoding of ID code information, thereby producing a problem in that the decoding cannot be performed.
This problem is particularly noticeable when the key cylinder 74 is disposed slantingly. It is a matter of course that, also when the key cylinder is disposed horizontally, this problem is produced.